1. Field of the Invention
This invention relates to load testing apparatus for testing the ability of a structural member to withstand uniform loads placed along the length of the structural member.
2. Description of the Prior Art
Prefabricated structural members are used in a number of industries, one of which is the mobile home industry. The roof of a mobile home is supported by any one of a variety of types of rafter or truss structures, depending upon the shape of the roof. Such structures include monopitch, bow truss, and A-type rafters.
It is necessary that such rafter structures be able to support a fairly substantial load placed on the roof of a mobile home. Accordingly, the load bearing capabilities of prefabricated structural members are tested on a regular basis. The test generally employed on prefabricated rafter or truss structures is to place each end of the rafter on a support and load the middle portion of the rafter at a series of points along the rafter with cement blocks or the like until the rafter breaks under the load. The amount of weight placed on the rafter and the spacing of the weights is predetermined by code, and the rafter must be able to support this load in order to be satisfactory. The applicable code specifies that the rafter be loaded with weights such as cement blocks or other suitable loading device such that any concentrated loads are one foot apart or less. An alternative to cement blocks in a series of point loads applied by individual hydraulic cylinders spaced along the truss or rafter.
The principal problem with the types of rafter testers used previously is that they test the rafter under unrealistic conditions by placing separate loads along the rafter structure. When a rafter structure is covered by the roof of a mobile home, the load placed on the rafter structure by snow or the like is uniformly distributed over the length of the rafter, and the stress generated by such a uniform load could be entirely different from the nature of the stress exerted at a series of individual positions along the rafter structure. Thus, such testers are inaccurate in determining the overall strength or weakness of the rafter structure.